1. Field of the Invention
This invention relates generally to electrodes and, more particularly, to a method and apparatus for an electrical discharge machining electrode.
2. Description of the Related Art
An axial flow rotary machine, such as a gas turbine engine for an aircraft, has a compression section, a combustion section, and a turbine section. An annular flow path for working medium gases extends axially through the sections of the engine. The gases are compressed in the compression section to raise their temperature and pressure. Fuel is burned with the working medium gases in the combustion section to further increase the temperature of the hot, pressurized gases. The hot, working medium gases are expanded through the turbine section to produce thrust and to extract energy as rotational work from the gases. The rotational work is transferred to the compression section to raise the pressure of the incoming gases.
The compression section and turbine section have a rotor that extends axially through the engine. The rotor includes arrays of rotor blades that transfer rotational work between the rotor and the hot working medium gases. Each rotor blade has an airfoil for this purpose which extends outwardly across the working medium flow path. The working medium gases are directed through the airfoils. The airfoils in the turbine section receive energy from the working medium gases and drive the rotor at high speeds about an axis of rotation. The airfoils in the compression section transfer this energy to the working medium gases to compress the gases as the airfoils are driven about the axis of rotation by the rotor.
The engine includes a stator disposed about the rotor. The stator has an outer case and arrays of stator vanes that extend inwardly across the working medium flowpath. The arrays of stator vanes are disposed upstream of the arrays of rotor blades in both the compression section and turbine section. The stator vanes each have an airfoil for guiding the working medium gases to the rotor blades as the gases are flowed along the flow path. The airfoils of the stator vanes and the rotor blades are designed to receive, interact with and discharge the working medium gases as the gases are flowed through the engine.
Blades, vanes, airfoils, such as, for example, stator vanes, rotor blades, and airfoils described above, and other parts are generally designed with one or more holes, such as, for example, cooling holes. Removing heat from a surface is highly dependent on air flow through the cooling holes. By providing shaped cooling holes to diffuse the exiting air, heat can be removed more efficiently, allowing the surfaces of blades, vanes, airfoils, and the like to withstand higher temperatures. EDM (electrical discharge machining) uses electrodes for providing precisely shaped cooling holes. FIG. 1 illustrates an exemplary electrode 1 having shaped teeth 2 containing diffuser sections 6 and metering sections 4. Exemplary electrode 1 concurrently produces as many shaped holes in the part as there are teeth 2.
Currently, electrodes are manufactured by a process of stamping or wire EDM. Wire EDM may be used for all electrode designs, however, is limited to low volume production due to the manufacturing process cycle time. Electrodes manufactured by stamping require tooling dies that have a long lead time, e.g., 10 months. Moreover, dies may have a tooling and design cost that exceeds $100,000.00. As a result, new airflow designs are undesirable due to expense and lengthy lead times of manufacturing new electrodes, and, thus, components such as, airfoils, vanes, and blades may be machined by existing electrodes having a less than optimum design. Furthermore, dies wear over time, adversely affecting the quality of electrodes made using the dies.
Accordingly, there is a need for an improved method of producing an electrical discharge machining electrode.
There is a further need for a method of producing an electrical discharge machining electrode having a reduced lead time and a reduced cost over the prior art.